A frequency-selective I/Q (inphase/quadratue) mismatch compensation method for wideband direct-conversion receivers (DCR) is proposed. The proposed algorithm can cancel the effect of analog frequency-dependent I/Q path imbalance and the frequency-selective channel by digital signal processing technique using training sequence. In this thesis, we derive a general signal model for an imbalanced analog front-end that reflects frequency-dependent mismatch of quadrature mixer and I/Q branch in wideband DCR. And, the algorithms, that estimates and compensates the channel and I/Q mismatch jointly, are proposed. Besides, simple estimation and compensation methods for orthogonal frequency division multiplexing (OFDM) systems that are popular wideband solutions nowadays are presented. Computer simulation results demonstrate the performance of proposed algorithm.